Stable fuel oil compositions



Patented Oct. 6, 1953 STABLE FUEL OIL COMPOSITIONS Edward Mitchell, Pittsburgh, Pa., and Alan P. Cramp, Petaluma. Calif., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware N Drawing.

Application June 7, 1951,

Serial No. 230,423

Claims.

This invention relates to stable fuel oil compositions. More particularly, the invention relates to stable fuel oil compositions which are composed of straight run and cracked oils.

When a heavy petroleum oil is subjected to catalytic cracking by any of the conventional processes such as the fixed bed, moving bed or fluid processes, wherein the heavy oil is contacted with a cracking catalyst such as a natural clay catalyst or a synthetic silica-alumina or silica-magnesia catalyst, the conversion products comprise not only gasoline hydrocarbons but also heavier distillate hydrocarbons, such as hydrocarbons boiling in the fuel oil range, that is, bydrocarbons boiling within the range of about 350 to about 750 F. Although the burning characteristics of such oils are fairly good, it is genorally the practice when using these catalytically cracked oils as fuels to mix them with straight run distillate oils of similar boiling range in order to produce mixed oils having better burning characteristics than catalytically cracked oils, and also in order to balance refinery production. In addition, thermally cracked distillates are sometimes mixed with straight run distillate oils of similar boiling range to produce fuel oils.

The problem of instability, as a practical matter, is troublesome primarily in the case of fuel oils consisting of mixtures of cracked and straight run oils. In the case of straight run distillates sludging or precipitation is not normally troublesome. However, in certain instances some straight run fuel oils will deposit sludge and may give trouble in service because of either inadequate or improper refining, or due to a natural instability attributable to some constituent not ordinarily present. This is exemplified by distillates containing large amounts of.sulfur, either as original components of the crude or present in the form of elemental sulfur and sulfur compounds added incidentally during the doctor treating of such distillates. In such cases, in addition to free sulfur and sulfur compounds, quantities of litharge may also remain in the oil. In addition, naphthenic acids may not be completely removed in the caustic washing process, and these may contribute to instability and the formation of precipitates in the subsequent storage and handling of such straight run fuels. It is believed that the problem encountered with straight run fuels is essentially one of oxidation and the formation of insoluble oxygenated compounds which results from contact with atmospheric and dissolved oxygen in the distillate. This problem is a different one from that encountered in the storage and use of mixed cracked and straight run oils.

In the case of cracked distillates the chemical nature of the components is considerably different from that of straight run materials, cracked distillates being, as a rule, highly aromatic and containing appreciable amounts of olefins and aromatic-olefin mixed-type compounds. Such compounds, by virtue of their unsaturated character, are particularly susceptible to polymerization reactions leading to the formation of relatively high molecular weight resinous or gum-like materials which may or may not contain appreciable amounts of oxygen. Although catalytically cracked stocks are relatively stable, thermally cracked stocks, depending upon the degree of cracking and on the type of charge stock, will precipitate sludge during storage. It is believed that this precipitation of sludge in thermally cracked stocks is mainly a result of oxidation and polymerization.

The tendency of fuel oils to cause the clogging of screens, conduits, and other parts of burners, therefore, varies with different fuel oils. However, it has been found that the tendency of a mixed cracked and straight run fuel oil to form objectionable sediment is greater than that of either oil alone. This is probably due to the fact that the decomposition products are less soluble in the mixed oil and therefore tend to precipitate out. Since the straight run component, being essentially parafiinic in nature, is a very poor solvent for the highly polymerized aromatic-olefin type compounds which are formed from the cracked component, it probably has the effect of reducing the solvent power of the cracked distillate itself for such polymeric material. As a result, precipitation of those materials will occur. It is believed that the sludge formed in such cases is of a different character from the sludge formed as a result of oxidation of straight run fuel oils.

The present invention relates to fuel oil compositions comprising mixed cracked and straight run distillate fuel oils, which compositions are of improved stability with respect to sludging and therefore of good appearance and adapted for effective use in fuel oil furnaces and as diesel fuels even after being stored for extended periods.

It has been discovered that such an improved mixed fuel oil composition can be obtained by incorporating in the mixed fuel oils a small amount of a polyvalent metal salt of a monoamide of'the class'consisting of 2,5-endoethylene- A -cyclohexene-l,S-dicarboxylic acid and alkylsubstitued 2,5-endoethylene-A -cyclohexene-l,6- dicarboxylic acids which contain not more than four alkyl groups each containing not more than six carbon atoms. The N-substituents of the monoamide are selected from the class of hydrogen and alkenyl radicals and contain a total of 8 to 22 carbon atoms; 1. e. where only one N-substituent is an alkyl or alkenyl radical, it

contains 8 to 22 carbon atoms and if both N-substituents are radicals of this class, they contain a total of 8 to 22 carbon atoms.

It is not clear as to what way the polyvalent metal salts of the class described function to improve the characteristics of the mixed fuel oil and therefore the invention is not limited toany theory of operation. It might-appear that they function as solubilizing agents for the sludge, but this function is more or less negatived by the fact that whereas a mixed-fuel oil in the absence of such a compound forms additional amounts of sludge so long asit is stored, at least over any feasible test storage period, the incorporation of a compound of this class in the oil inhibits the formation of additional sludge even after some sludge has been formed, although the already formed sludge doesnot disappear. We have discovered, however, that-by adding asmall amount of a compound of this class .to a mixed fuel. oil containing an amount of sludgemekingthe oil undesirable for use in a householdburner because of sludge deposits, the oil can be employed in such a burner without leaving the undesirable deposits. In this case it appears that although the sludge does not disappear, its characteristics are so changed as to prevent its deposition on a sulting reaction product is then reacted with an amine to form the monoamide and the polyvalent metal salt is then formed. The alpha-terpinene salt of this invention can be prepared by using dipentene or A -menthadiene. Dipentene and the alpha-beta ethylenic dicarboxylic acid, containing not more than eight carbon atoms are reacted at a temperature sufiiciently high to rearrange the double bonds of dipentene to a coniugated system. The resulting reaction product can then be reacted with the amine to form the monoamide. The metal salt of the monoamide can then be prepared. The temperature employed to rearrange the double bonds of dipentene is usually between about 280-F.'and the bOil n point of the dipentene. say between about 280 F. and 375 F.

During the reaction, 1. e. when the dicarboxylic acid and diene are reacted, the two compounds join together forming an endoethylene bridge. The product formed, depending upon the cyclohexadiene employed, is believed to be principally either 2,5-endoethylene-A -cyclohexene-L6-dicarboxylic acid, or the substituted dicarboxylic acid having not more than four alkyl groups each of not more than six carbon atoms. The alkyl groups may be any suitable lower alkyl groups such as methyl, ethyl. isopropyl, tertiary or secondary butyl, amyl andlhexyl groups. Thus, when alpha-terpinene and maleic anhydride are used, the product formed is believed to be 2,5- endoethylene 2 methyl 5 isopropyl A cyclohexene-l,B-dicarboxylic acid. The fuel oil addition agents of the present invention are the metal salts of the .monoamides of said resulting acids.

As statedprevionsly, the alpha-beta ethylenic dicarboxylic acid employed in accordance with this invention is one containing not more than eight carbon atoms. Suitable acids are maleic, citraconic, fumaric, glutaconic and their geometric isomers such asimesaconic and the like. It is understood, unless otherwise indicated, that acids and acid anhydrides are both included when reference is made to theacid or the anhydride since these two are equivalents.

Diene compounds adapted for use are, cyclohexadiene-L3, 5-methy1 cyclohexadiene-1,3, the dimethyl cyclohexadienes such as 4,6-dimethyl cyclohexadiene-1,3 and 2,4-dimethyl cyclohexadiene-1',3, the trimethyl cyclohexadienessuchas 4,5,5-trime'thyl cyclohexadiene-Ls, the methyl isopropyl dienes such .as alpha-terpinene, also, 1,5 dimethyl 3 ethyl cyclohexadiene 1.3. 1 methyl '3 ethyl 4 isopropyl cyclohexa- (Ilene-1,3, l-methyl-S-isobutyl cyclohexadiene-l,3. and l-methyl-S-n-hexyl .cyclohexadiene-lfi.

An a'lkyl-substituted '2,5-endoethylene-A cyclohexene 1,6-dicarboxy1ic acid prepared by the reaction between a cyclohexadiene-.1,3 .compound and an alpha-beta ethylenic dicarboxylic acid having an alkyl group attached to the carbon atom-to which a carboxylgroupis attached, will also contain an alkylgroup attached toa carbon atom to which a carboxyl groupattached. It will lie-understood that all of the cyclohexene- 1,6-dicarboxylic acids of this class which contain four alkyl groups must have one of these groups attached to a carbon atom to which a carboxyl group is attached. .Moreover. such a carbon atom may contain an alkyl substituent in any case. For example, when cyclohexadiene 1,3 is condensed with citraconic acid, the resu1ting cyclohexene-1,6-dicarboxylic acid will contain one alkyl'substituent and this a methyl group attached to a carbon atom to which a carboxyl group is also attached. Also, it will benoted that'when an acid, such as glutaconic acid, in which the two carboxyl groups are not both attached to the carbon atoms forming the ethylenic double bond, is employed, the final cyclohexene dicarboxylic acid will be one in whicha carboxyl group is linked to the cyclohexene ring through an alkylene radical. Such compounds are equivalent to those in which both carboxyl groups are attached directly to carbon atoms of the cyclohexene ring and are included when the 2,5 endoethylene A cyclohexene -'1,6 dicarboxylic acids are referred to, unless otherwise indicated.

The amines which can be employed in the formation of the monoamides mentioned heretofore are primary alkyl or alkenyl amines having from 8 to 22 carbon atoms, and secondary alkyl and alkenyl amines having a total of from 8 to 22 carbon atoms. Examples of suitable amines are octyl amine, decyl amine, undecyl amine, dodecyl (lauryl) amine, tetradecyl amine, octadecyl amine, diamyl amine, dibutyl amine, octenyl amine, decenyl amine, Nbutyl decenyl amine, undecenyl amine, dodecenyl amine, tetradecenyl amine, hexadecenyl amine, and octadecenyl amine. Mixtures of amines such as are commercially available are especially desirable, for example, mixtures of primary alkyl amines derived from fatty acids and having from approximately 8 to 22 carbon atoms. The monoamides formed thus have two nitrogen substituents selected from hydrogen, alkyl or alkenyl radicals, and wherein the total number of carbon atoms in the N-substituents is from 8 to 22. In addition, at least one substituent is an organic radical of said group.

The polyvalent metal salts of the monoamides can be prepared directly, that is by neutralization or treatment with the metal oxide; or they can be prepared indirectly by double decomposition. Metals employed in preparing these salts are barium, magnesium, calcium, nickel, zinc, lead, copper, strontium, chromium, and the like.

The following examples illustrate the various methods of preparing the improvement agents and improved compositions containing the same.

EXAhdPLE I A typical procedure for preparing salts was first to heat 38 parts by weight of dipentene (technical, boiling 48 to 52 C. at 6 mm. pressure) at 300 F. for 30 minutes. At a rate sufiicient to maintain the temperature over 275 F., 26 parts by weight of maleic anhydride were added over a period of ten to thirty minutes, and the mixture was stirred at 300 F. to 320 F. for about thirty minutes. The reaction was somewhat exothermic and maintained its own temperature for about ten to thirty minutes. The reaction product thus obtained was then cooled to approximately 200 F. and 60.5 parts by weight of octadecyl amine were added at a rate such that the temperature did not exceed 220 F. This addition took about minutes. After this addition the mixture was stirred at a temperature of 200 F. to 220 F. for fifteen minutes. Then, 6.35 parts by weight of magnesium oxide (about excess) were slowly added and the mixture was stirred at a temperature of 200 F. to 220 F. for a period of from one to two hours. The final product was extracted with one-third to one half gallon of benzene, filtered and the benzene was distilled ofi.

EXAMPLE II In this example 27 parts by weight of alphaterpinene were heated to a temperature from 310 to 320 F. Then, 20.2 parts by weight of maleic anhydride were slowly added and the heating was continued at 310 F. to 320 F. for one hour. The reactants were then cooled to 200 F. and 46.4 parts by weight of octadecyl amine were added, the temperature being maintained at 200 F. for thirty minutes. Then 5.28 parts by weight of magnesium oxide were added and the reaction mixture was agitated at a temperature of 210 F. to 215 F. for at least one hour. The magaluminum, bismuth, iron,

nesium salt thus formed was extracted with a volatile solvent, filtered and the solvent removed by distillation. The magnesium salt prepared in accordance with this example was an amber tacky solid having the following properties:

Percent ash (oxide) 4to5 Percent nitrogen 3.14 Sp. gr. 77/60 F 0.9405 Viscosity Solid Neut. No 78.9 Sap. No 82.2 Acetyl No 83.7 Iodine No 28.2 Melting point F 300 EXAMPLE III In this example 21.4 parts by weight of alphaterpinene were heated to a temperature from 310 F. to 320 F. Then, 15.4 parts by weight of maleic anhydride were slowly added and the heating was continued at 310 F. to 320 F. for one hour. The reactants were then cooled to 200 F. and 35.8 parts by weight of octadecyl amine were added, the temperature being maintained at 200 F. for thirty minutes. Then 27.4 parts by weight of barium hydroxide were added and the reaction mixture was agitated at a temperature of 210 F. to 215 F. for at least one hour. The barium salt thus formed was extracted with a volatile solvent, filtered and the solvent removed by distillation. The barium salt prepared in accordance with this example was a red tacky solid. The per cent ash, as the oxide, was 20.1.

EXAMPLE IV In this example 27.6 parts by weight of alphaterpinene were heated to a temperature from 310 to 320 P. Then, 20.0 parts by weight of maleic anhydride were slowly added and the heating was continued at 310 F. to 320 F. for one hour. The reactants were then cooled to 200 F. and 46.3 parts by weight of octadecyl amine were added, the temperature being maintained at 200 F. for thirty minutes. Then 6.1 parts by weight of calcium oxide were added and the reaction mixture was agitated at a temperature of 210 F. to 215 F. for at least one hour. The calcium salt thus formed was extracted with a volatile solvent, filtered and the solvent removed by distillation. The calcium salt prepared in accordance with this example was a solid having a milky appearance. The per cent ash, as the oxide, was 5.0.

EXAMPLE V In this example 19.8 parts by weight of alphaterpinene were heated to a temperature from 310 F. to 320 F. Then, 14.6 parts by weight of maleic anhydride were slowly added and the heating continued at 310 F. to 320 F. for one hour. The reactants were then cooled to 200 F. and 38.0 parts by weight of octadecyl amine were added, the temperature being maintained at 200 F. for thirty minutes. After the addition of the amine, the reactants were dispersed in water and neutralized with six parts by weight of sodium hydroxide. The nickel salt was then prepared by reacting the sodium salt thus prepared with 21.2 parts by weight of an aqueous nickel nitrate solution. The nickel salt prepared in accordance with this example was a green tacky solid. The per cent ash, as the oxide, was 8.0.

EXAMPLE VI In this example 34 parts by weight of alpha- .terpinene were heated to a temperature irom 310 F. to 320F. Then 24.5 parts by weight of maleic anhydride were slowly added and the heating was continued at 310 F. to 320 F. for one hour. The reactants were then cooled to 200 vF. and 50 parts by weight of octadecyl amine EXAMPLE VII In this example parts by weight of alphaterpinene were heated to a temperature from 310 F. to 320 F. Then, 7.2 parts by weightof maleic anhydride were slowly added and the heating continued at 310 F. to 320 F. for one hour. The reactants were cooled to 200 and 20.5 parts by weight of a mixture of amines were added, the temperature being maintained at 200 F. for thirty minutes. The composition of the mixture of amines was per cent hexadecyl amine, 25 per cent octadecyl amine and per cent octadecenylamines. Then, 6 parts by weight of calcium hydroxide mixed with one part by weight of water were added and the reaction mixture was agitated at a temperature of 210 F. to 215 F, for at least one hour. The calcium salt thus formed was extracted with a volatile solvent, filtered and the solvent removed by distillation.

The addition of the compound 'in very small amounts has been found to produce excellent results. Thus, our composition comprises a major amount of the mixed straight run and cracked distillate fuel oils and a minor amount, sufficient to inhibit sludge deposition, of a polyvalent metal salt of the class described above. Fully efiective results are obtained when using between about 0.025 and about 0.1 per cent of the additive by weight of the mixed fuel oil for addition-even to mixed oils having high sulfur content and pronounced sludging tendencies. Moreover, satisfactory results are obtained when using as little as 0.005 per cent by weight on the mixed fuel oil. In this instance, in many cases full inhibition of sludge formation is not obtained but the mixed oil is satisfactory for use because the additive changes the physical, and perhaps chemical, nature of the sludge so that it does not cause rapid clogging of screens and other parts of burners. While larger quantities than 0.1 per cent can be used, no advantage appears to result. The addition of excessive amounts will necessarily increase the ash and undistillable residue in the oil, and is not usually required for normal storage conditions.

The polyvalent metal salt may be incorporated in the mixed fuel oil in any suitable manner. For example, it may be added to either or both of the cracked or straight run oils prior to mixing the two or it may be added to the mixed oil. When the compound is incorporated in the mixed oil, it is unnecessary to do this immediately after mixing the oil as the compound is eflective even after some sludge has formed. It will usually be preferable to add the compound prior to any sludge formation as this will either eliminate sludge formation, or reduce the amount of sludge which will be formed, depending upon the specific characteristics .of the oils employed in making up themixed oil and uponthe amount of the com- .poundladded. The compound can be added as such, but it is preferred to employ it in the form of. a concentrated solution in an oil carrier. After addition, some circulation of the mixed oil is desirable to insure the early production of a uniform composition, .but this is not absolutely necessary.

It is em a ized that the problem with which the present invention is concerned exists primarily when a cracked oil and a straight run oil are-combined in such proportions as to cause a substantial effect such as previously described. The invention is important when the ratio of the volume of thecracked oil to the straight run oil .is within therange of-9z1 to 1:9. It is especially advantageous when applied to mixed oils containing these oils inavolumeratio within the range of 4:1 to.1:4.

In the following tables there are :given the results of .Light Stability Tests made on the mixed fuel oils of the character indicated, in the absence of an additive, and containing compounds of the class disclosed above. The percentages of each compound used in the tests are weight percentages of the compound in-the oil. A No. 2 oil is defined-in ASTM-Standards on Petroleum Products and Lubrican 0396-481. The term No. 2 indicates a'distillate-oil for general purpose domestic heating .for use in burners not requiring a No. 1 iueloil, and having the following properties: Flash point F'.-100 or legal (min), pour point 'F-.'20 (max.), water and sediment per cent by vol-0.1 (max.), carbon residue per cent by weight-0.35 on 10% residuum, distillation temperature F. point-- 675 (max.), viscosity Saybolt Universal Seconds at F.40 (max.), gravity API26 (min.) and maximum sulfur content-1 per cent.

The light stability test was carried out by exposing a 100cc. sample of the oil to be tested to a light source rich in ultra-violet rays, for periods of 4 hours alternated with periods of 2 hours-during which the oil was stored in the dark. The test was completed after 40 hours exposure to the light. At the end of each dark storage period the samples were examined for the presence of precipitated sediment or sludge. The exposure to light was accomplished by putting samples of iuel oilin 4-ounce bottles which were .unstoppered to allow access of air. These bottles were placed within a circular metal enclosure at a distance of 22 inches from the light source which was a Westinghouse 400 watt type DH-l mercury vapor lamp mounted vertically in the center of the housing. It was found that a temperature rise of approximately 20 F. occurs during the exposure period. The interval of darkness was necessary to allow any dispersed sludge to settle and tcpermit oxygen to replace any used up in the light-induced reaction. The efiect of the exposure to light was judged by swirling the bottle and estimating the quantity of precipitate which had settled. This was recorded as trace, light, medium or heavy. The salt employed in the following light stability tests was the magnesium salt of the monoamide of 2,5-endoethylene 2 methyl 5 isopropyl-A cyclohexene-1,6-dicarboxylic acid wherein the two N-substituents are hydrogen and an octadecyl radical. This salt is referred toin the following tables as Compound A.

TABLE I Light stalnlzty test No. of hours of ultra-violet light required to sludge samples to $32 3 Sample Description End of Test Trace Light Medium Heavy (40 hours) 50/50 Blend Eastern Venezuela 4 12 28 40 Heavy.

Straight Run and Fluid Catalytically Cracked (Blend N o 1). Blend No. 1 Plus 0.05% by Weight 4 Trace.

on the Mixed Fuel Oil of Compound A. Blend No. 1 Plus 0.1% by Weight 4 Trace+.

on the Mixed Fuel Oil of Compound A. 50/50 Blend Eastern Venezuela 4 8 28 Medlumt Straight Run and Fluid Catalytieally Cracked (Blend No 2). Blend No. 2 Plus 0.025% y 4 Tracet Weight on the Mixed Fuel Oil of Compound A. Blend No. 2 Plus 0.05% by Weight 4 Trace+.

on the Mixed Fuel Oil of Compound A. Blend No. 2 Plus 0.1% by Weight 4 Traceon the Mixed Fuel Oil oi Compound A.

A storage test was also carried out to determine 25 the stability of the fuel oil compositions disclosed herein. This test was carried out by pouring 1500 cubic centimeters of the fuel to be tested into a two-quart Mason jar and immersing an 8 inch by 1 inch by 3; inch SAE 1020 cold rolled steel strip in the oil. The steel surface to oil ratio approximates that existing in a 55 gallon steel drum. The jar was then closed with a vented lid and was stored in total darkness.

30 noted.

out as rapidly as possible in subdued light. The extent of deterioration of the fuel was determined by the amount of precipitate observed and designated as trace, light, medium or heavy. Any staining or corrosion of the steel strip was also In the following tables there are tabulated the results obtained in storage tests on the oils alone and stabilized fuel oil compositions of the invention. The salt employed in these laboratory stor- Periodically sampling and testing were carried 35 age tests was Compound A.

TABLE II Laboratory storage tests on mixed No. 2 fuel oils Make-up oi Fuels, Percent by Vol;

Eastern Venezuela Straight Run 50* so Fluid Catalytieally Cracked Distillate" 50" 50 50. Concentration of Additive: Percent by 0.05. 0.1,

weight on oil. Storage Time:

1 month- Sludge Trace None None. Appearance of Steel O OK OK. 3 months- Sludge Medium Trace None. Appearance of Steel OK 0K 0K. 6 months- Sludge Heavy Light Trac Appearance of Steel Stained (4 months).. Slight Stain OK. 12 months- Slmloa Heavy Medium Tm Appearance 0! S l Stained Stained (10 months)..- 0K.

Blend No. 1.

TABLE III.

Laboratory storage tests on mixed No. 2 fuel oils Make-up of Fuels, Percent by Vol.2

Eastern Venezuela Straight Run..- 50" 5o Fluid Catalytically Cracked Dis- 502- 5m tillate. Concentration of Additive: Percent 0.05... 0.1-... 0,025,

by weight on oil. Storage Time:

1 e i N N u go one one None Tra Ap ance ofshwl OK. 0 O OK f I: 3 s i d L' ht+ N u ge 1g one.- None Medium Trace. email ceof Steel Stained OK 0 Slight Stai.n Very Slight Stain.

qlnfin'n Heavy. None" None-. Hea L ht Appearance of Steel Stained (5 mouths)-- OK.-- 0 Stained stint stain. 7% monthsqlnri n Heavy None.. None Appearance of SteeL Stained OK... 0

"Blend N o. 2.

'"Blend No. 3. c

From the results given in the foregoing tables it will be seen that the mixed oils possess poor stability properties. These results also show that mixtures of straight run and catalytically cracked oils are materially improved with respect to stability to sludge formation by the addition of a polyvalent metal salt of the class disclosed above. Major improvement is obtained by the addition of from 0.025 per cent to 0.1 per cent by weight based on the oil. Also stability to sludge formation is obtained when larger amounts are employed, but for normal storage conditions such larger amounts are not necessary. Therefore, when positive control of sludge formation is desired, it is preferred to employ at least 0.025 per cent by weight on the oil of the polyvalent metal salt and in most cases it is not necessary to em:- ploy more than 0.1 per cent by weight based on the oil.

The tests employed in obtaining the data set out in the tables are especially severe tests of the compounded oils and the results are given in terms of the quantity of sludge deposited without j regard to the nature of the sludge. In practice, however, the quantity of sludge formed is frequently not as important as the physical characteristics of the sludge. The. addition of a very small amount of a compound or the class described to a mixed fuel oil affects the characteristics of the sludge, making it lighter and appar: ently more easily dispersed. so. that the sludge deposition is avoided or at least materially lessened. To accomplishvariation in the nature of the sludge as well as some control over the actual formation of sludge, as. little as,i0.005 per cent or less by weight onthe mixed oils of the polyvalent metal salt can be used. Consequently, as previously pointed out, we generally prefer to employ the salt in an amount equal to about 0.005 to about 0.1 per cent by weightonthe mixed oils.

It will be understood that in place of the compound used in the tests, other members of the class of compounds disclosed above may be used to prepare fuel oil compositions of substantially the same improved properties. Particularly valuable compounds are the magnesium and barium salts of the monoamide of 2,5-endoethylene- 2-methyl isopropyl-A -cyclohexene-1,6-dicarboxylic acid wherein the two N-substituents are hydrogen and a hexadecyl radical.

If desired, the stable fuel oil compositions may contain in addition to the compounds previously discussed, oxidation inhibitors, flash point control agents, corrosion inhibitors, anti-foam agents, ignition quality improvers, combustion improvers and other additives adapted" to iniprove the oils in one or. more respects.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the, spirit or scope thereof and therefore only such limitations should be imposed as are indicatedin the-appended claims.

We claim:

1. A fuel oil composition comprising a major proportion of a mixture of straight run and cracked distillate fuel oils tending to deposit sludge, and a minor amount, suflicient to inhibit sludge deposition from said mixture of oils, of. a polyvalent metal salt of a monoamide of a dicarboxylic acid, wherein the twoIN-substituents are selected from the group consisting ofhydrogen, alkyl and alkenyl radicals, at least one substituent being an organic radical of said group and the total number of carbon atoms in the N- substituents is 8 to 22, and wherein said dicarboxylic acid is selected from the group consisting of unsubstituted and alkyl-substituted 2,5-endo ethylene-A -cyclohexene-1,6-dicarboxylic acids, said anal-substituted dicarboxylic acids having not more than four alkyl groups each having not more than six carbon atoms.

2. A fuel oil composition comprising a major proportion of a mixture of straight run and cracked distillate fuel oils tending to deposit sludge, and a minor amount, sufficient to inhibit sludge deposition from said mixture ofoils, of a polyvalent metal salt of amonoamide of 2,5- endoethylene-Z-methyl 5- isopropyl-Am-cycloe hexene-l,6-dicarboxylic acid, wherein the two N- substituents are selected from the, group consiste. ing of hydrogen, alkyl and alkenyl radicals, at least, one substituent being an organic radical of said group, and the total number of carbon atoms in the N -s ubs tituents is 8 to 22.

3. A fuel oil composition comprising a major proportion of a mixture of straight run and cracked distillate fuel oils tending to deposit sludge, and a minor amount, sufiicient to inhibit sludge deposition from said mixture of oils, of the magnesium salt of a monoamide of 2,5-endoethylene-2emethyl-5-isopropyl-A -cyclohexene 1,6-dicarboxylic acid, wherein the two N-substituents are hydrogen and anv octadecyl radical.

4. A fuel oil composition comprisinga major amount of a. mixture of straightrun and cracked distillate fuel oils tending to deposit sludge, and about 0.005 to 0.1 per cent by weight on the mixe ture of a polyvalent metal salt of a monoamide of a dicarboxylic acid, wherein the two N-substituents are selected from the group consisting of hydrogen, alkyl and alkenyl radicals, at least one substituent being an organic radical of said group, and the total number of carbon atoms in the N- substituents is 8 to 22, and wherein said dicarboxylic acid is selected from the group consisting of unsubstituted and alkyl-substituted 2,5-endoethylene-A -cyclohexene-1,6-dicarboxylic acids, said substituted dicarboxylic acid having not more than four alkyl groups each having not more than six carbon atoms.

5. A fuel oil composition comprising a major amount of a mixture of straight run and cracked distillate fuel oils tending to deposit sludge, and about 0.005 to 0.1 per cent by weight on the mixture of a polyvalent metal salt of a monoamide of 2,5-endoethy1ene 2 methyl-5-is0pr0pyl-A cyclohexene-1,6-dicarboxylic acid, wherein the two N-substituents are selected fromv the group consisting of hydrogen, alkyl and alkenyl radicals, at least one substituent being an organic radical of said group, and the total number of carbon atoms in the N-substituents is 8 to 22.

6. A fuel oil composition comprising a major amount of a mixture of straight run and cracked distillate fuel oils tending to deposit sludge, and about 0.025 to 0.1 percentby, weight of the mixed fuel oil of a polyvalent metal salt of a monoamide of 2,5-endoethylene 2-- methyl-5-isopropyl-A cyclohexene-1,6-dicarboxylic acid, wherein the two N-substituents are selected from the group consisting of hydrogen, alkyl and alkenyl radicals, at least one substituent. being an organic radical of said group, and. the total number of carbon atoms in the N-substituentsis 8 to 22.

'7. A fuel oil composition comprising a major amount of a mixture of straight run and catalytically cracked distillate fuel oils tending to deposit sludge, andv about 0.025 to 0.1 per cent by 13 weight of the mixed fuel oil of the magnesium salt of a monoamide of 2,5-endoethylene-2-methyl--isopropyl A -cyclohexene-1,6-dicarboXYlic acid, wherein the two N-substituents are hydrogen and an octadecyl radical.

8. A fuel oil composition comprising a major amount of a mixture of straight run and catalytically cracked distillate fuel oils tending to deposit sludge, and about 0.025 to 0.1 per cent by weight of the mixed fuel oil of the aluminum salt of a monoamide of 2,5-endoethylene-2-methyl-5-isopropyl A -cyclohexene-L6-dicarboxylic acid, wherein the two N-substituents are hydrogen and an octadecyl radical.

9. A process for treating a composition consisting essentially of a mixture of straight run and cracked distillate fuel oils from which sludge has begun to deposit to prevent further substantial deposition of sludge which comprises introducing into the fuel composition containing sludge a minor amount sufficient to inhibit further sludge deposition of a polyvalent metal salt of a monoamide of a dicarboxylic acid, wherein the two N-substituents are selected from the group consisting of hydrogen, alkyl and alkenyl radicals, at least one substituent being an organic radical of said group, and the total number of carbon atoms in the N-substituents is 8 to 22, and wherein said dicarboxylic acid is selected from the group consisting of unsubstituted and alkyl-substituted 2,5-endoethylene-A -cyclohexene-1,6-dicarboxylic acids, said alkyl-substituted dicarboxylic acids having not more than four allwl groups each having not more than six carbon atoms.

10. A process for treating a composition consisting essentially of a mixture of straight run and cracked distillate fuel oils from which sludge has begun to deposit to prevent further substantial deposition of sludge which comprises introducing into the fuel composition containing sludge about 0.005 to 0.1 per cent by weight of a polyvalent metal salt of a monoamide of a dicarboxylic acid, wherein the two N-substituents are selected from the group consisting of hydrogen, alkyl and alkenyl radicals, at least one substituent being an organic radical of said group, and the total number of carbon atoms in the N- substituents is 8 to 22, and wherein said dicarboxylic acid is selected from the group consisting of unsubstituted and alkyl-substituted 2,5-endoethylene-A -cyclohexene1,6-dicarboxylic acids, said alkyl-substituted dicarboxylic acids having not more than four alkyl groups each having not more than six carbon atoms.

EDWARD MITCHELL. ALAN P. CRAMP.

References Cited in the flle of this patent UNITED STATES PATENTS Number Name Date 2,301,795 Proell Nov. 10, 1942 2,458,425 Rocchini Jan. 4, 1949 

1. A FUEL OIL COMPOSITION COMPRISING A MAJOR PROPORTION OF A MIXTURE OF STRAIGHT RUN AND CRACKED DISTILLATE FUEL OILS TENDING TO DEPOSIT SLUDGE, AND A MINOR AMOUNT, SUFFICIENT TO INHIBIT SLUDGE DEPOSITION FROM SAID MIXTURE OF OILS, OF A POLYVALENT METAL SALT OF A MONOAMIDE OF A DICARBOXYLIC ACID, WHEREIN THE TWO N-SUBSTITUENTS ARE SELECTED FROM THE GROUP CONSISTING OF HYDROGEN, ALKYL AND ALKENYL RADICALS, AT LEAST ONE SUBSTITUENT BEING AN ORGANIC RADICAL OF SAID GROUP AND THE TOTAL NUMBER OF CARBON ATOMS IN THE NSUBSTITUENTS IS 8 TO 22, AND WHEREIN SAID DICARBOXYLIC ACID IS SELECTED FROM THE GROUP CONSISTING OF ETHYLENE-$3:4-CYCLOHEXENE-1,6-DICARBOXYLIC ACIDS, SAID ALKYL-SUBSTITUTED DICARBOXYLIC ACIDS HAVING NOT MORE THAN FOUR ALKYL GROUPS EACH HAVING NOT MORE THAN SIX CARBON ATOMS. 